Background:  We wanted to evaluate the role of HHV-8 T-cell responses in the pathophysiology of HHV-8-related tumors.

Methods:  For a study of T-cell responses to HHV-8, we enrolled 23 HIV/HHV-8 co-infected asymptomatic patients (long-term non-progressors or chronically infected patients), and 22 patients with HIV-associated or classical Kaposi’s sarcoma all seropositive for HHV-8. These responses were analyzsed with an IFN-γ ELISpot assay. We tested 60 HHV-8 peptides:  predicted LANA-1 epitopes (9 and 10 mers) binding HLA*0201 molecule, 15-mer peptides overlapping by 10 aa covering the entire K12 sequence and exons 1 to 3 in K15, and 5 previously described epitopes in K12, GpH, Gp35/37, and GpB. The threshold of positive responses was 50 SFC/10⁶ PBMC above background.

Results:  T-cell responses against HHV-8 could be detected in 14/23 (61%) asymptomatic patients while only 5/22 (18%) Kaposi’s sarcoma patients had positive responses. Moreover, the median frequency of HHV-8-specific T cells was statistically higher in the group of asymptomatic patients than in Kaposi’s sarcoma patients:  377 (70 to 1455) and 95 (65 to 130) SFC/106 PBMC, respectively (p = 0,019). CD4 cell counts were not significantly different in both groups (p = 0,8438) and were not correlated to HHV-8-specific T-cell numbers. Among Kaposi’s sarcoma  patients, all responses to HHV-8 were observed in patients with classic Kaposi’s sarcoma (5/14, 36%) and none of the HIV-associated Kaposi’s sarcoma patients displayed T-cell-specific T-cell response to HHV-8 (0/8, 0%). The specific T-cell responses of the sub-group of HIV⁺ patients with Kaposi’s sarcoma (CD4 = 378/mm³) had been compared with those of HHV-8 carriers chronically infected by HIV (CD4 = 301/mm³). The median frequency of specific T cells is also statistically lower in the sub-group of HIV patients with Kaposi’s sarcoma:  0 and 420 (125 to 490) SFC/106 PBMC, respectively (p = 0.0273). Correlation with HHV-8 viral load will be analyzed. Finally, using this set of peptides in ELISpot assay, we find 5 new HHV-8-specific CD8 epitopes:  two 9-mers in K15 protein, one 15-mers in K12 protein and two 9-mers in LANA-1 protein. The HLA-restricted elements will be discussed.

Conclusions:  HIV-infected patients with symptomatic HHV-8 disease  have lower HHV-8 T cells than asymptomatic HHV-8 carriers independently of their CD4 cell numbers. These results suggest that a specific defect of such HHV-8-specific response is associated to Kaposi sarcoma during HIV infection.

Keywords: T cell responses; Human Herpesvirus-8; Kaposi's sarcoma